io_uring: finish IOU_OK -> IOU_COMPLETE transition

IOU_COMPLETE is more descriptive, in that it explicitly says that the
return value means "please post a completion for this request". This
patch completes the transition from IOU_OK to IOU_COMPLETE, replacing
existing IOU_OK users.

This is a purely mechanical change.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/msg_ring.c

@@ -328,7 +328,7 @@ done:
 		req_set_fail(req);
 	}
 	io_req_set_res(req, ret, 0);
-	return IOU_OK;
+	return IOU_COMPLETE;
 }
 
 int io_uring_sync_msg_ring(struct io_uring_sqe *sqe)